System for improving the energy efficiency in hydraulic systems, piston accumulator and pressure accumulator provided for such a system

ABSTRACT

The invention relates to a system for improving the energy efficiency in hydraulic systems, comprising an actuator ( 49 ) which, in an operating state, operates as a consumer of hydraulic energy and, in a different operating state, as a generator of hydraulic energy, and a hydraulic accumulator ( 1 ) which, when in an operating state of the actuator ( 49 ), can be charged by the same for storing energy and, when in a different operating state, can be discharged for delivering energy to the actuator ( 49 ). The invention is characterized in that at least one hydraulic accumulator in the form of an adjustable hydropneumatic piston accumulator ( 1 ) is provided, in which a are formed a plurality of pressure chambers ( 19, 21, 23, 25 ) which adjoin effective surfaces ( 11, 13, 15, 17 ) of different sizes on the fluid side of the accumulator piston ( 5 ), and an adjusting arrangement ( 51 ) is provided which connects a selected pressure chamber ( 19, 21, 23, 25 ) or a plurality of selected pressure chambers ( 19, 21, 23, 25 ) of the piston accumulator ( 1 ) to the actuator ( 49 ) as a function of the pressure level that prevails respectively on the gas side of the piston accumulator ( 1 ) and on the actuator ( 49 ).

The invention relates to a system for improving the energy efficiency in hydraulic systems, having an actuator which, in one operating state, functions as a consumer of hydraulic energy and in another operating state, functions as a generator of hydraulic energy, and having a hydraulic accumulator which, when in one operating state of the actuator, can be charged by the same for the storage of energy, and when in another operating state, can be discharged for the delivery of energy to the actuator. In addition, the invention relates to a hydropneumatic piston accumulator for use with such a system and a pressure accumulator.

Given the increasing scarcity of resources and the increased efforts to save energy associated therewith, systems of the above type are becoming increasingly important. Thus such systems are used in hydraulic devices and systems for example, in which actuators in the form of working cylinders are provided, which generate movements against a load as consumers, or which generate energy from load forces for storage in the hydraulic accumulator. Thus for example in lifting and lowering applications, the potential energy of a lifted load can be converted into hydraulic energy, which may be stored and recycled. Hydraulic hybrid systems for rotary drives are a further field of application. In this case, the actuator has a motor pump unit between a drive motor and a working hydraulics or hydrostatic drive, which motor pump unit functions as a consumer or as a generator of hydraulic energy for storage and recycling in the hydraulic accumulator in corresponding operating states.

Regardless of the application, the efficiency of the energy conversion in the known systems leaves something to be desired. One reason for this is the dependence of the charging and discharging processes of the hydraulic accumulator on the respective system pressure. More specifically, the hydraulic accumulator can still only be charged when the system pressure is greater than the gas pressure found in the accumulator on the gas side. When the system pressure cannot be built up in the respective operating situation of the actuator, it is not possible to acquire energy in the accumulator. The discharge process of the accumulator is subject to the restriction that energy can only be fed back from the accumulator when the accumulator pressure is still greater than the current system pressure. In addition, there is the problem that in the case of an accumulator pressure that is greater than the currently needed system pressure, the pressure levels of the accumulator and the system must be balanced by means of valves, so that the energy contained in the differential pressure between the accumulator pressure and the system pressure is lost due to throttling losses.

In view of these problems, the object of the invention is to provide a system of the type under consideration, a piston accumulator and a pressure accumulator, which make a more favorable energy conversion possible.

This object is achieved according to the invention by a system that has the features of claim 1 in its entirety. Advantageous embodiments of the system are apparent from the dependent claims 2 to 11.

Accordingly, an essential feature of the invention is that at least one hydraulic accumulator is provided, which offers a preferably discontinuous option for adjustment, in that the accumulator provides a plurality of pressure chambers, which are adjacent to effective surfaces on the fluid side of the accumulator piston having different sizes, wherein an adjustment assembly is provided, which connects a selected pressure chamber or a plurality of selected pressure chambers of the piston accumulator to the actuator as a function of the respective pressure level prevailing on the gas side of the piston accumulator. This results in the possibility of recycling energy independent of the pre-charge pressure on the gas side of the accumulator, and independent of the respective load pressure, because the respectively desired pressure level on the accumulator can be used for charging and discharging by selecting an effective surface of suitable size. An optimum energy conversion is thereby possible for all operating conditions.

The use of a “multi-step accumulator” of this kind also opens up the possibility of influencing the load time by means of selecting the effective surfaces. Selecting a small surface at a constant volume flow results in a short charge time for the accumulator, while selecting a larger surface at a constant volume flow results in a longer charge time. A finer or coarser pressure gradation can be achieved by forming a larger or smaller number of pressure chambers of different effective piston surfaces. More than one accumulator with different pressure chambers may also be provided in order to achieve an especially high degree of resolution.

In an especially advantageous manner, the adjustment arrangement may be associated with a control logic, which process the signals from sensor devices for the control of the valves associated with the adjustment arrangement, which signals represent the pressure level on the gas side of the piston accumulator and the respective operating state of the actuator. In so doing, the logic controls the energy transformation, in that it is decided how to charge or discharge the accumulator according to the load at the actuator and the load state at the accumulator. In so doing, there is the possibility that the user may influence the logic with his own requirements, and thereby influence the operating characteristics of the system.

In terms of the design of the piston accumulator, the assembly may be advantageously made in such a way that, for the formation of effective surfaces having different sizes, the accumulator piston is designed as a stepped piston or step-shaped, and has partial piston surfaces on the fluid side thereof that are adjacent to cylinder surfaces, wherein the accumulator housing has corresponding mating surfaces that are adjacent to cylinder surfaces, which mating surfaces, together with the partial piston surfaces associated therewith, each delimit separate pressure chambers.

Effective surfaces on the accumulator piston and mating surfaces on the accumulator housing are preferably disposed in steps or levels that are disposed such that they are spaced axially apart from one another.

At least one of the pressure chambers can be disposed while also maintaining the axial offset in the interior of the piston. In this respect, a guiding spike for the cylinder is formed, protruding from the cylinder housing. The piston is therefore guided both from outside and from within. The installation height of the piston accumulator is thus shortened and the guidance of the piston substantially improved.

Effective surfaces and mating surfaces may be provided in the form of annular surfaces or circular surfaces, which are concentrically disposed relative to the longitudinal axis.

In terms of the control of the pressure chambers of the piston accumulator, the assembly may be advantageously made in such a way that the adjustment arrangement has switching valves, by means of which valves respective pressure chambers of the piston accumulator, which are selected for charging or discharging, can be connected to the actuator, and the remaining pressure chambers can be connected to the tank. Thus a selected pressure chamber or a combination of selected pressure chambers for charging or discharging can be connected to the actuator by means of the control logic, while pressure chambers that are not selected can be emptied into the tank without pressure during the discharge, and can be refilled from the tank again during the charging of active pressure chambers.

In terms of the provision of signals of the control logic, the arrangement can be advantageously made such that the assigned sensor device has at least pressure sensors, which provide signals to the control logic, which represent the filling pressure on the gas side of the piston accumulator and the system pressure at the actuator. In addition, the sensor device may have a displacement measuring device, with which the stroke of the accumulator piston may preferably be detected.

Pursuant to claim 11, the subject matter of the invention also includes a hydropneumatic piston accumulator for a system according to one of the claims 1 to 10, wherein, in the accumulator housing, which guides the accumulator piston axial such that it is axially movable, a plurality of pressure chambers are formed, which are adjacent to effective surfaces having different sizes on the fluid side of the piston.

Further embodiments of the hydropneumatic piston accumulator are defined in the dependent claims 12 to 21.

For the formation of effective surfaces having different sizes, the accumulator piston may be designed as a stepped piston or step-shaped, and have partial piston surfaces on the fluid side thereof that are adjacent to cylinder surfaces. The accumulator housing may have corresponding mating surfaces that are adjacent to cylinder surfaces, which mating surfaces, together with the partial piston surfaces associated therewith, each delimit separate pressure chambers.

The effective surfaces on the accumulator piston and the mating surfaces on the accumulator housing may be disposed in steps or levels that are disposed such that they are spaced axially apart from one another.

At least one, preferably at least two; of the pressure chambers may be disposed in the interior of the accumulator piston while maintaining the axial spacing.

The effective surfaces and the mating surfaces may be provided in the form of annular surfaces or circular surfaces, which are concentrically disposed relative to the longitudinal axis.

A step-shaped bottom part may be provided, wherein the accumulator piston and the bottom part have overlapping wall parts.

All pressure chambers may be separated from one another in a media-tight manner within the accumulator housing.

The pressure chamber disposed in the longitudinal axis of the accumulator housing may be encompassed by a step-shaped part of the accumulator piston, in particular the inner piston thereof. The step-shaped part of the accumulator piston may delimit a further pressure chamber on the outer circumference with a cylinder surface and additional parts of the accumulator piston.

A middle extension of the bottom part, in particular an inner piston, which is designed as a displacement piston, may retract during a relative movement of the accumulator piston and bottom part towards one another in the step-shaped part of the accumulator piston, in particular in the inner piston thereof.

The object is also achieved by a pressure accumulator having the features of claim 22. Advantageous embodiments of the pressure accumulator embodiments of the system are apparent from the dependent claims 23 and 24.

The pressure accumulator, in particular designed in the manner of a hydropneumatic piston accumulator, has an accumulator housing, which has a top part and a bottom part at the ends thereof, and in which at least one accumulator piston is disposed such that it is longitudinally displaceable, which piston separates a first media side, in particular a gas side, from a second media side, in particular a fluid side. At least one of the two media sides has pressure chambers that are separated from one another, disposed concentrically relative to a longitudinal axis of the accumulator housing. The respective pressure chambers, which are delimited by the accumulator piston and/or by the bottom part, undergo a change in volume, provided that the bottom part retracts into the pressure chambers of the accumulator piston and the accumulator piston retracts into the pressure chambers of the bottom part in a relative movement of the accumulator piston and bottom part towards one another, starting from a maximum position in which at least one of the pressure chambers is maximally filled with a medium, in the direction of a minimum position in which the at least one pressure chamber is comparatively less filled. According to the invention, all pressure chambers are separated from one another in a media-tight manner within the accumulator housing.

The pressure chamber disposed in the longitudinal axis of the accumulator housing may be encompassed by a step-shaped part of the accumulator piston, in particular the inner piston thereof. The step-shaped part of the accumulator piston may delimit a further pressure chamber on the outer circumference with a cylinder surface and additional parts of the accumulator piston.

A middle extension of the bottom part, in particular an inner piston, which is designed as a displacement piston, may retract during a relative movement of the accumulator piston and bottom part towards one another in the step-shaped part of the accumulator piston, in particular in the inner piston thereof.

The invention is explained in detail below based on the embodiments illustrated in the drawings. Shown are:

FIG. 1 a highly schematic, simplified longitudinal section of an embodiment of a hydropneumatic piston accumulator in a multi-step design for use in the system according to the invention;

FIG. 2 a schematic diagram, which shows the piston accumulator from FIG. 1 in conjunction with associated system components of the system according to the invention;

FIG. 3 the piston accumulator in conjunction with a hydraulic circuit diagram, shown in a symbol representation, of an embodiment of the system for a lifting and lowering application;

FIG. 4 an illustration of a modified embodiment of the lifting and lowering application corresponding to FIG. 3;

FIG. 5 the piston accumulator in conjunction with a hydraulic circuit diagram, shown in a symbol representation, for the use of the system according to the invention for a hydraulic hybrid system for rotatory drives; and

FIG. 6 an alternative embodiment of the hydropneumatic piston accumulator.

The schematic, simplified illustration of a hydropneumatic piston accumulator 1 shown in FIG. 1 has an accumulator piston 5 that is guided in an accumulator housing 3 such that it is axially movable, which accumulator piston separates a gas side 7 on which a filling connector 9 is located, from pressure chambers on the fluid side in an accumulator housing 3. The accumulator piston 5 is designed in the manner of a stepped piston in such a way that said accumulator piston, in cooperation with correspondingly stepped sections of the of the accumulator housing 3, delimits fluid-side pressure chambers 19, 21, 23 and 25, which are adjacent to effective surfaces having different sizes on the fluid side of the accumulator piston 5. In FIG. 1, these effective surfaces are designated as 11, 13, 15 and 17 from the smallest surface to the largest surface. The effective surfaces 11, 13 and 15 are thereby each formed by annular surfaces that are concentric relative to the longitudinal axis, which annular surfaces enclose the innermost effective surface 17 in the form of a circular surface. Pressure chambers 19, 21 or 23 respectively, which are adjacent to the effective surfaces 11, 13 and 15, are delimited by mating surfaces 27 or 29 or 31 respectively of the accumulator housing 3 as well as by cylinder surfaces 35 of the cylinder housing 3 and cylinder surfaces 37 on the accumulator piston 5. The pressure chamber 25, which is adjacent to the effective surface 17, is delimited by a mating surface 33 of the accumulator housing 3 as well as by a cylinder surface 39 of the accumulator piston 5.

A fluid connection 41, 43, 45 or 47 respectively is provided for each pressure chamber 19, 21, 23, 25. As the effective surfaces 11, 13, 15 and 17 are disposed on the accumulator piston 5, the associated mating surfaces 27, 29, 31 or 33 respectively are disposed on the accumulator housing 3 in steps that are axially spaced apart from one another.

FIG. 2 shows the piston accumulator 1 in conjunction with system components allocated thereto, wherein an actuator 49 is operatively connected to an adjustment arrangement 51. As already noted, the actuator 49 may be a component of a lifting and lowering arrangement for example, or of a hydraulic hybrid systems for rotary drives. A control logic 53 is allocated to the adjustment arrangement 51, which control logic actuates a valve assembly 57 of the adjustment arrangement 51 by means of a control and regulating unit 55. As is explained in greater detail based on FIGS. 3 to 5, the valve assembly 57 has switching valves, which create selected fluid connections between the actuator 49 and the fluid ports 41, 43, 45, 47 of the piston accumulator 1, in order to selectively activate the pressure chambers 19, 21, 23 and 25 for charging or discharging processes. To this end, the control logic 53 processes signals, which are provided by sensor devices and which represent the operating conditions of the actuator 49 and piston accumulator 1. Of these sensor devices, only one pressure sensor 59 on the filling connector 9 of the piston accumulator 1 is shown in FIG. 2.

FIG. 3 shows the system according to the invention in conjunction with a lifting and lowering arrangement, wherein the actuator has a working cylinder 58 for lifting and lowering a load 61. A pressure sensor 63, which detects the load pressure, and a path sensor 65, which detects the lifting and lowering speed, are provided on the working cylinder 58 in order to generate the signals that are to be processed by the control logic 53. A hydraulic pump 67, safeguarded on the output side by a pressure relief valve 69, is connected to a main line 71 of the adjustment arrangement 51 that controls the system pressure. This pump has a connecting line 73, 75, 77 and 80 for the connection between the main line 71 and each of the fluid ports 41, 43, 45 and 47 of the piston accumulator 1. A valve group, designated by the symbols v₁, v₂, etc., is located in each of the connecting lines, which valve group can be actuated by the control logic 53, wherein each valve group comprises two fast-switching 2/2-way valves, which are designated as 79 and 81, and in the case of the valve group v₁ to v₄, are designated with the indices 1 to 4. The associated connecting line can be connected to or blocked on the associated fluid ports of the piston accumulator 1 by means of the directional valves 81. The respective connecting line 73, 75, 77, 80 can be connected to the tank 83 by means of the directional valves 79. In addition, each pressure chamber 19, 21, 23, 25 is safeguarded by a pressure relief valve, which is not shown in greater detail.

In the case of a lifting process, the main line 71 can be connected to the working cylinder 58, which is safeguarded by a pressure relief valve 86, by means of a valve, which is designed as a proportional throttle valve 87 for the control of the lifting speed, as well as by means of a fluid filter 85. The lifting movement is made with the aid of the energy stored in the piston accumulator by means of a discharge process from a selected pressure chamber 19, 21, 23, 25 or from a plurality of selected pressure chambers, which have the appropriate pressure level for the lifting movement of the load 61. In the case of the lowering movement, the potential energy of the load 61 is stored as hydraulic energy in the piston accumulator 1, in that a charging process occurs by means of an application-dependent proportional throttle valve 84 that adjusts the lowering speed, and a selected connecting line 73, 75, 77, 80 or by means of a plurality of selected connecting lines, to a respective fluid port 41, 43, 45, 47, wherein one or a plurality of the directional valves 81 is or are opened respectively, and directional valves 79 in connecting lines that are not selected establish the connection to the tank 83. Through this connection, non-selected pressure chambers 19, 21, 23, 25 of the piston accumulator 1 are unpressurized during the discharging processes, and can be refilled from the tank 83 during recharging processes. A directional valve 88 located on the main line 71 makes it possible to depressurize or empty the system as needed.

In order to lower a load with energy recovery, the load pressure on the cylinder 58 is transmitted to the control logic 53 during operation by means of the pressure sensor 63, and likewise, the gas pressure on the accumulator 1 is detected by means of the pressure sensor 59. Using this information, the feedback control can decide how the available potential energy of the cylinder 58 can be optimally fed back into the accumulator 1. In the case of low loads, a large effective surface may be selected in order to charge the accumulator to a high pressure level. If there is a high load 61 on the cylinder 58, the accumulator 1 is charged with a small effective surface. The lowering speed of the load is adjusted by means of the proportional throttle valve 84.

The load compensation effected by the system may be done discontinuously by selecting and/or switching the suitable effective surfaces, wherein, with a sufficiently large number of pressure levels made available in the accumulator 1, it is possible to achieve a resolution that allows the load to be lowered smoothly. In so doing, the throttle valve 84 can smooth out the discontinuity with a pressure compensator. In order to lift a load 61 in the case of a charged piston accumulator 1, either with or without the aid of the pump 67, the appropriate effective surface, or the appropriate effective surfaces, is or are selected according to the load 61 to the cylinder 58 as a function of the gas pressure in the accumulator 1. In order to smoothly initiate the movement of the load 61, a smaller pressure level is preferably initially selected. The speed for raising the load 61 is adjusted by means of the proportional throttle valve 87, wherein the pressure differential is kept as small as possible by means of the suitable selection of the effective surfaces of the accumulator 1, so that a low-loss conversion of the storage energy is possible during the lifting work.

The embodiment in FIG. 4 differs from the example in FIG. 3 only in that a pressure compensator 89 or 90 respectively is provided on each of the proportional throttle valves 84 and 87, in order to generate a constant pressure differential on the associated proportional throttle valve 84, 87. Jumps to the pressure difference at the respective proportional throttle valve 84, 87 may be compensated for by switching the effective surfaces of the accumulator 1.

Instead of the proportional throttle valves 84, 87, these jumps may also be controlled by pulse-width modulation in the case that fast-switching directional valves 79 and 81 are used, whereby a desired average volume flow can be adjusted as a function of the impulse modulation or of the pulse duty factor.

FIG. 5 shows the system according to the invention in use in a hydraulic hybrid system for rotary drives, wherein a motor pump unit 91 is provided as an actuator, the pump shaft 92 of which is coupled on one side with a drive source, for example an internal combustion engine 93, and on the other side with a rotary driven device 94. This device may be a working hydraulics, a traction drive or the like, i.e. it may be a device that, in one operating state, functions as a consumer of hydraulic energy and in other operating states, for example during braking of the traction drive, may generate a corresponding torque on the pump shaft 92 as a generator of hydraulic energy. The pressure side of the motor pump unit 91 is connected to a main line 71 of the adjustment arrangement 51 that controls the system pressure by means of a non-return valve 95. This adjustment arrangement has a connecting line 73, 75, 77, 80 for each connection between the main line 71 and the fluid ports 41, 43, 45 and 47 of the piston accumulator 1. A valve group, designated by the symbols v₁, v₂ etc., which can be actuated by the control logic 53, is located in each of the connecting lines, wherein each valve group comprises two fast-switching 2/2-way valves, which are designated as 79 and 81, and in the case of the valve group v₁ to v₄, are designated with the indices 1 to 4. The respective associated connecting line 73, 75, 77, 80 can be connected to or blocked on the associated fluid port 41, 43, 45 or 47 respectively of the piston accumulator 1 by means of the directional valves 81.1 to 81.4. The respective connecting line can be connected to the tank 83 by means of the directional valves 79.1 to 79.4.

In order to generate the signals, which are to be processed by the control logic 53, a pressure sensor 59 that detects a pressure level on the gas side is provided on the filling connector 9 of the piston accumulator 1, a pressure sensor 63 that detects the system pressure is provided on the main line 71, and a speed sensor 96 is provided on the drive motor 93. Based on these signals, the control logic 53 decides which of the connecting lines 73, 75, 77 or 80 or which combination of these lines will create the connection between the main line 71 and the respectively associated fluid port 41, 43, 45, 47 on the piston accumulator 1. In so doing, a selection is made as to which of the pressure chambers 19, 21, 23, 25, or which combination of these pressure chambers, is best suited for a charging process or discharging process at the respective prevailing pressure level of the system pressure (main line 71) and of the accumulator 1. In the case of the discharging process, the recovered energy is returned to the suction side of the motor pump unit 91 from the main line 71, which is safeguarded by a pressure relief valve 86, by means of a switching valve 97. In the case of charging processes, the switching valve 97 is closed and a connecting line, or a plurality of the connecting lines 73, 75, 77, 80, is/are activated by means of the directional valves 81.1 to 81.4, wherein each of the associated directional valves 79.1 to 79.4 are closed. On the other hand, in the case of each of the non-activated connecting lines 73, 75, 77, 80, the directional valves 79.1 to 79.4 establish the connection to the tank 83, so that the connected, non-selected pressure chambers 19, 21, 23 or 25 of the accumulator 1 are without pressure during discharging processes, and can be refilled from the tank 83 during charging processes. In the case of changing system conditions, the respectively selected combination of the effective surfaces 11, 13, 15, 17 may be changed during the charging processes or discharging processes. An inverse shuttle valve 99 is provided in order to remove the excess quantity of fluid in the circuit that is discharged from the accumulator 1 during the discharging processes from the now depressurized downstream side of the motor pump unit 91 to the tank 83. In the case of charging processes, the upstream side of the motor pump unit 91 may also be connected to the tank 83 for refilling processes by means of this shuttle valve.

The schematic, simplified illustration of an alternative embodiment of the hydropneumatic piston accumulator 101 shown in FIG. 6 has an accumulator piston 105, which is guided in a tubular accumulator housing 103 such that the piston can be axially displaced, said accumulator piston separating a gas side 107 in the accumulator housing 103, on which side a filling connector 109 in the form of an excentrically disposed bore is located, from fluid-side pressure chambers 119, 121, 123, 125. The accumulator piston 105 is movably disposed between a sleeve-like extension 185 of the gas-side top part 149 and a fluid-side bottom part 151. The top part 149 and the bottom part 151 are supported, and to this extent, fixed on projections 153 by means of snap rings 155 on grooves 157 on the inner circumference of the accumulator housing 103. The bottom part 151 and the accumulator piston 105 are designed such that they are step-shaped and having wall parts 159, 161, wherein the wall parts 159, 161 overlap and two of the pressure chambers 119, 121 are axially held by two notional planes 163, 163 in the longitudinal direction shown in FIG. 6. Both the accumulator piston 105 and also the bottom part 151 have inner pistons 171, 173 that are held by means of pins 167 in recesses 169. The inner pistons 171, 173 likewise have wall parts 175, 177, which overlap one another and overlap with the wall parts 159, 161 of the accumulator piston 105 and bottom part 151.

Radial seals 179 are provided between the accumulator housing 103 and the top part 149, the accumulator piston 105, and the bottom part 151, respectively. Additional radial seals 181 are disposed between the accumulator piston 105 and the bottom part 151, as well as the inner pistons 171, 173. The pressure chambers 119, 121, 123, 125 are adjacent to effective surfaces having different sizes on the fluid side of the accumulator piston 105 the inner piston 171 thereof, respectively. In FIG. 6, these effective surfaces are designated as 111, 113, 115, 117 from the largest surface to the smallest surface. In so doing, the effective surfaces 111, 113, 115 are each formed by annular surfaces, which are concentrically disposed relative to the longitudinal axis 183, which annular surfaces enclose the innermost effective surface 117 in the form of a circular surface. Pressure chambers 119, 121, 123, which are adjacent to the effective surfaces 111, 113, 115, are delimited by mating surfaces 127, 129, 131 of the bottom part 151 or of the inner piston 173 thereof, as well as by a cylinder surface 135 of the cylinder housing 103 and cylinder surfaces 137 on the accumulator piston 105, the bottom part 151 and the inner piston 171, 173.

The pressure chamber 125, which is adjacent to the effective surface 117, is delimited by a mating surface 133 of the inner piston 173 on the bottom part side, as well as by a cylinder surface 137 of the inner piston 171 on the accumulator piston side. A fluid port 141, 143, 145, 147, in each case in the form of a bore in the bottom part 151, is provided for each pressure chamber 119, 121, 123, 125. Adjacent to the top part 149, a tubular sleeve 185 is used as a stop for the accumulator piston 105 in the accumulator housing 103. The sleeve 185 contacts the accumulator housing 103 on the outside. In addition, a displacement measuring device 187 is provided in order that the distance A, from the top part 149 to the accumulator piston 105, may be determined at any time. Moreover, a wire 191 is attached to an eyelet 189 on the accumulator piston 105, which may be extended from a sensor device 193. Moreover, a pressure measuring device, not shown in greater detail, may be integrated within the sleeve 185. 

1. A system for improving the energy efficiency in hydraulic systems, having an actuator (49) which, in one operating state, functions as a consumer of hydraulic energy and in another operating state, functions as a generator of hydraulic energy, and having a hydraulic accumulator (1; 101) which, when in one operating state of the actuator (49), can be charged by the same for the storage of energy, and when in another operating state, can be discharged for the delivery of energy to the actuator (49), characterized in that at least one hydraulic accumulator, in the form of a, preferably discontinuously, adjustable hydropneumatic piston accumulator (1; 101), is provided, in which a plurality of pressure chambers (19, 21, 23, 25; 119, 121, 123, 125) are formed, which are adjacent to effective surfaces (11, 13, 15, 17; 111, 113, 115, 117) of different sizes on the fluid side of the accumulator piston (5; 105), and in that an adjustment arrangement (51) is provided, which connects a selected pressure chamber (19, 21, 23, 25; 119, 121, 123, 125) or a plurality of selected pressure chambers (19, 21, 23, 25; 119, 121, 123, 125) of the piston accumulator (1; 101) to the actuator (49) as a function of the respective pressure level prevailing on the gas side of the piston accumulator (1; 101) and on the actuator (49).
 2. The system according to claim 1, characterized in that a control logic (53) is associated with the adjustment arrangement (51), which control logic processes the signals from sensor devices (59, 63) for the control of the valves (79, 81) associated with the adjustment arrangement (51), which signals represent the pressure level on the gas side of the piston accumulator (1; 101) and the respective operating state of the actuator (49).
 3. The system according to claim 1, characterized in that, for the formation of different effective surfaces (11, 13, 15, 17; 111, 113, 115, 117), the accumulator piston (5; 105) is designed as a stepped piston, or cup-shaped, and has partial piston surfaces on the fluid side thereof that are adjacent to cylinder surfaces (35, 37, 39; 135, 137, 139), and in that the accumulator housing (3; 103) has corresponding mating surfaces (27, 29, 31, 33; 127, 129, 131, 133) that are adjacent to cylinder surfaces (35, 37; 135, 137), which mating surfaces, together with the partial piston surfaces associated therewith, each delimit separate pressure chambers (19, 21, 23, 25; 119,121, 123, 125).
 4. The system according to claim 1, characterized in that effective surfaces (11, 13, 15, 17; 111,113,115, 117) on the accumulator piston (5; 105) and mating surfaces (27, 29, 31, 33; 127, 129, 131, 133) on the accumulator housing (3; 103) are disposed in steps or levels that are located such that they are spaced axially apart from one another.
 5. The system according to claim 4, characterized in that at least one, preferably at least two, of the pressure chambers (23, 25) is/are disposed in the interior of the accumulator piston (5) while maintaining the axial spacing.
 6. The system according to claim 1, characterized in that effective surfaces (11, 13, 15, 17; 111, 113, 115, 117) and mating surfaces (27, 29, 31, 33; 127, 129, 131, 133) may be provided in the form of annular surfaces or circular surfaces, which are concentrically disposed relative to the longitudinal axis (183) of the accumulator.
 7. The system according to claim 1, characterized in that the adjustment arrangement (51) has switching valves (79, 81), by means of which valves respective pressure chambers (19, 21, 23, 25; 119, 121, 123, 125), which are selected for charging or discharging, can be connected to the actuator (49), and the remaining pressure chambers (19, 21, 23, 25; 119, 121,123, 125) can be connected to the tank (83).
 8. The system according to claim 1, characterized in that the sensor devices have at least pressure sensors (59, 63), which provide signals for the control logic (53), which indicate the filling pressure on the gas side of the piston accumulator (1; 101) and the system pressure at the actuator (49).
 9. The system according to claim 1, characterized in that the sensor devices have at least one displacement measuring device (187), which provides signals for the control logic (53), which represent the stroke of the accumulator piston (105).
 10. The system according to claim 1, characterized in that the system is a component of a hydraulic system, which has at least one working cylinder (58) as an actuator for lifting and lowering a load (61).
 11. The system according to claim 1, characterized in that this system is a component of a hydraulic hybrid system in which at least one hydraulic pump motor unit (91) is provided as an actuator.
 12. A hydropneumatic piston accumulator for a system according to claim 1, characterized in that in the accumulator housing (3; 103), which guides the accumulator piston (5; 105) such that it is axially movable, a plurality of pressure chambers (19, 21, 23, 25; 119, 121, 123, 125) are formed, which are adjacent to effective surfaces having different sizes (11, 13, 15, 17; 111, 113, 115, 117) on the fluid side of the piston (5; 105).
 13. The piston accumulator according to claim 12, characterized in that, for the formation of effective surfaces (11, 13, 15, 17; 111, 113, 115, 117) having different sizes, the accumulator piston (5) is designed as a stepped piston or cup-shaped, and has partial piston surfaces on the fluid side thereof that are adjacent to cylinder surfaces (35, 37, 39; 135, 137, 139), and that the accumulator housing (3; 103) has corresponding mating surfaces (27, 29, 31, 33; 127, 129, 131, 133) that are adjacent to cylinder surfaces (35, 37; 135, 137), which mating surfaces, together with the partial piston surfaces associated therewith, each delimit separate pressure chambers (19, 21, 23, 25; 119,121,123, 125).
 14. The piston accumulator according to claim 12, characterized in that effective surfaces (11, 13, 15, 17; 111, 113, 115, 117) on the accumulator piston (5; 105) and mating surfaces (27, 29, 31, 33; 127, 129, 131, 133) on the accumulator housing (3; 103) are disposed in steps or levels that are located such that they are spaced axially apart from one another.
 15. The piston accumulator according to claim 14, characterized in that at least one, preferably at least two, of the pressure chambers (23, 25) is/are disposed in the interior of the accumulator piston (5) while maintaining the axial spacing.
 16. The piston accumulator according to claim 12, characterized in that effective surfaces (11, 13, 15, 17; 111, 113, 115, 117) and mating surfaces (27, 29, 31, 33; 127, 129, 131, 133) may be provided in the form of annular surfaces or circular surfaces, which are concentrically disposed relative to the longitudinal axis (183) of the accumulator.
 17. The piston accumulator according to claim 12, characterized in that a step-shaped bottom part (151) is provided, wherein the accumulator piston (105) and the bottom part (151) have overlapping wall parts (159, 161).
 18. The piston accumulator according to claim 17, characterized in that inner pistons (171, 173) are provided in the accumulator piston (105) and in the bottom part (151), wherein the wall parts (159, 161, 175, 177) of the inner pistons (171, 173), of the accumulator piston (105) and of the bottom part (151) preferably overlap.
 19. The piston accumulator according to claim 12, characterized in that all pressure chambers (19, 21, 23, 25; 119, 121, 123, 125) separated from one another in a media-tight manner within the accumulator housing (3; 103).
 20. The piston accumulator according to claim 12, characterized in that the pressure chamber (25; 125), which is disposed in the longitudinal axis (185) of the accumulator housing, is encompassed by a step-shaped part of the accumulator piston (5; 105), in particular the inner piston (171) thereof, wherein the step-shaped part of the accumulator piston (5; 105) delimits a further pressure chamber (21; 121) on the outer circumference with a cylinder surface (37; 137) and additional parts of the accumulator piston (5; 105).
 21. The piston accumulator according to claim 12, characterized in that a middle extension of the bottom part (151), in particular an inner piston (173), which is designed as a displacement piston, retracts during a relative movement of the accumulator piston (105) and bottom part (151) towards one another in the step-shaped part of the accumulator piston (105), in particular in the inner piston (171) thereof.
 22. A pressure accumulator, in particular designed in the manner of a hydropneumatic piston accumulator, having an accumulator housing (3; 103), which has a top part (149) and a bottom part (151) at the ends thereof, and in which at least one accumulator piston (3; 103) is disposed such that it is longitudinally displaceable, which piston separates a first media side, in particular a gas side (7; 107), from a second media side, in particular a fluid side (19, 21, 23, 25; 119, 121, 123, 125), at least one of the two media sides has pressure chambers (19, 21, 23, 25; 119, 121, 123, 125) that are separated from one another, disposed concentrically relative to a longitudinal axis (185) of the accumulator housing (3; 103), wherein the respective pressure chambers (19, 21, 23, 25; 119, 121, 123, 125), which are delimited by the accumulator piston (5; 105) and/or by the bottom part (151), undergo a change in volume, provided that the bottom part (151) retracts into the pressure chambers (19, 21, 23, 25; 119, 121, 123, 125) of the accumulator piston (5; 105) and the accumulator piston (5; 105) retracts into the pressure chambers (19, 21, 23, 25; 119, 121, 123, 125) of the bottom part (151) in a relative movement of the accumulator piston (5; 105) and the bottom part (151) towards one another starting from a maximum position, in which at least one of the pressure chambers (19, 21, 23, 25; 119, 121, 123, 125) is maximally filled with a medium, in the direction of a minimum position, in which the at least one pressure chamber (19, 21, 23, 25; 119, 121, 123, 125) is comparatively less filled, characterized in that all pressure chambers (19, 21, 23, 25; 119, 121, 123, 125) are separated from one another in a media-tight manner within the accumulator housing (3; 103).
 23. The pressure accumulator according to claim 22, characterized in that the pressure chamber (25; 125) disposed in the longitudinal axis (185) of the accumulator housing is encompassed by a step-shaped part of the accumulator piston (5; 105), in particular the inner piston (171) thereof, wherein the step-shaped part of the accumulator piston (5; 105) delimits a further pressure chamber (21; 121) on the outer circumference with a cylinder surface (37; 137) and additional parts of the accumulator piston (5; 105).
 24. The pressure accumulator according to claim 22, characterized in that a middle extension of the bottom part (151), in particular an inner piston (173) designed as a displacement piston, retracts during a relative movement of the accumulator piston (105) and bottom part (151) towards one another in the step-shaped part of the accumulator piston (105), in particular in the inner piston (171) thereof. 